1. Field of the Invention
The present invention relates to an optical transmission apparatus, such as an ONU (Optical Network Unit) used in a PON (Passive Optical Network), that uses an optical interface module to perform optical communication, an optical transmission system, an optical transmission apparatus control method, and a recording medium on which a program for the apparatus is recorded.
2. Description of Related Art
A configuration of a typical dual-rate ONU will be described with reference to FIG. 1. A typical dual-rate ONU as shown in FIG. 1 includes an optical module unit 501 that transmits and receives optical signals to and from an optical transmission line. The optical module unit 501 includes a receiver (Rx) 503 capable of receiving optical signals 502 with the same wavelength at two different bit rates and a transmitter (Tx) 504. This configuration enables the exemplary ONU shown in FIG. 1 to receive optical signals with the same wavelength at dual rates of, 1 Gbps and 2 Gbps.
In an art related to the present invention, packets received at a subscriber connection apparatus on a PON are distributed to multiple PON termination circuits and multiple user network interfaces (UNIs) by a multiplexer/demultiplexer, thereby reducing equipment costs per UNI line (see for example Japanese Patent Laid Open Publication No. 2004-104376).
Problems with the existing techniques describe above will be described below.
The typical dual-rate ONU apparatus described has the following problems.
A first problem is that the optical module cannot deal with different service modes that use downstream optical signals with different wavelengths because its receiver 503 supports different bit rates provided that the signals are in the same wavelength band.
A second problem is that the optical module cannot deal with different service modes that use upstream optical signals with different wavelengths and different bit rates because its transmitter 504 supports only the same bit rate in the same wavelength band.
When a subscriber wants to migrate to a different service type, the subscriber has to replace the whole ONU with a new one since the ONU cannot deal with optical signals in different wavelength bands as described above. The replaced ONU is discarded and therefore the problem of recycling of discarded ONUs has arisen.
The technique disclosed in Japanese Patent Laid Open Publication No. 2004-104376 is intended to reduce equipment costs by allowing an optical network interface to be shared by multiple PON termination circuits and multiple UNIs and does not make consideration to use a removable optical interface module to allow the apparatus to respond to a change from a type of service to another that uses a different light wavelength.